Ivabradine ameliorates cardiomyopathy progression in a Duchenne muscular dystrophy model rat

Chronic administration of ivabradine improves cardiac Ca handling and function in a rat model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD), a severe muscle disease caused by mutations in the gene encoding for the intracellular protein dystrophin, is associated with impaired cardiac function and arrhythmias. A causative factor for complications in the dystrophic heart is abnormal calcium (Ca) handling in ventricular cardiomyocytes, and restoration of normal Ca homeostasis has emerged as therapeutic strategy. Here, we used a rodent model of DMD, the dystrophin-deficient DMDmdx rat, to test the following hypothesis: chronic administration of ivabradine (IVA), a drug clinically approved for the treatment of heart failure, improves Ca handling in dystrophic ventricular cardiomyocytes and thereby enhances contractile performance in the dystrophic heart. Intracellular Ca measurements revealed that 4-months administration of IVA to DMDmdx rats significantly improves Ca handling properties in dystrophic ventricular cardiomyocytes. In particular, IVA treatment increased electrically-evoked Ca transients and speeded their decay. This suggested enhanced sarcoplasmic reticulum Ca release and faster removal of Ca from the cytosol. Chronic IVA administration also enhanced the sarcoplasmic reticulum Ca load. Transthoracic echocardiography revealed a significant improvement of cardiac systolic function in IVA-treated DMDmdx rats. Thus, left ventricular ejection fraction and fractional shortening were enhanced, and end-systolic as well as end-diastolic diameters were diminished by the drug. Finally, chronic IVA administration neither significantly attenuated cardiac fibrosis and apoptosis, nor was vascular function improved by the drug. Collectively our findings suggest that long-term IVA administration enhances contractile function in the dystrophic heart by improvement of Ca handling in ventricular cardiomyocytes. Chronic IVA administration may be beneficial for DMD patients.

Ivabradine restores tonic cardiovascular autonomic control and reduces tachycardia, hypertension and left ventricular inflammation in post-weaning protein malnourished rats

Malnutrition results in autonomic imbalance and heart hypertrophy. Overexpression of hyperpolarization-activated cyclic nucleotide-gated channels (HCN) in the left ventricles (LV) is linked to hypertrophied hearts and abnormal myocardium automaticity. Given that ivabradine (IVA) has emerging pleiotropic effects, in addition to the widely known bradycardic response, this study evaluated if IVA treatment could repair the autonomic control and cardiac damages in malnourished rats.

AIM

Assess the impact of IVA on tonic cardiovascular autonomic control and its relationship with hemodynamics regulation, LV inflammation, and HCN gene expression in post-weaning protein malnutrition condition.

MAIN METHODS

After weaning, male rats were divided into control (CG; 22 % protein) and malnourished (MG; 6 % protein) groups. At 35 days, groups were subdivided into CG-PBS, CG-IVA, MG-PBS and MG-IVA (PBS 1 ml/kg or IVA 1 mg/kg) received during 8 days. We performed jugular vein cannulation and electrode implant for drug delivery and ECG registration to assess tonic cardiovascular autonomic control; femoral cannulation for blood pressure (BP) and heart rate (HR) assessment; and LV collection to evaluate ventricular remodeling and HCN gene expression investigation.

KEY FINDINGS

Malnutrition induced BP and HR increases, sympathetic system dominance, and LV remodeling without affecting HCN gene expression. IVA reversed the cardiovascular autonomic imbalance; prevented hypertension and tachycardia; and inhibited the LV inflammatory process and fiber thickening caused by malnutrition.

SIGNIFICANCE

Our findings suggest that ivabradine protects against malnutrition-mediated cardiovascular damage. Moreover, our results propose these effects were not attributed to HCN expression changes, but rather to IVA pleiotropic effects on autonomic control and inflammation.